In manufacturing of active-matrix LCD devices, defective pixels are “repaired”. As a method for repairing after an assembling process, a following technique has been proposed, for example. A repair-use region or repair circuit is arranged at each pixel dot. On repairing, the repair-use region is irradiated with laser beams from reverse side of transmissive array substrate as to melt a metal pattern in the repair-use region and induce short circuiting of the pixel electrode with a gate wiring pattern. In this way, a luminous dot of the defective pixel is converted to a dark dot. Please see JP-1997(09)-113936A, or Japan's patent application publication No. 9-113936, for example.
On repairing the LCD device of OCB mode, two categories of techniques have been conceived. First category among them is those converting the luminous dot to the dark dot by applying a direct-current voltage onto a pixel electrode; and second category is those severing out a conductive pattern for forming a pixel capacitance (storage capacitance, Cs) from a pixel electrode.
The repairing techniques of the first category have following problems. FIG. 7 shows a relationship between applied voltage and transmittance for a liquid crystal layer in pixels of the OCB-mode LCD. Displaying of black tone or of tones close to the black tone requires direct-current voltage value in vicinity of a given value “Vb” for applying to the liquid crystal layer. Voltage value applied to the liquid crystal layer is difference between a common voltage (Vcom) on a counter electrode and a voltage applied on a pixel electrode; and hence, displaying of black or of near-black tone requires applying onto the pixel electrode a voltage in vicinity of either one of two voltages (Vcom+Vb, Vcom−Vb) that are smaller and larger than the common voltage (Vcom) by the given value “Vb”. Thus, freedom or flexibility on setting a direct-current voltage to be applied on a defective pixel dot is limited. Moreover, some wirings in a pattern layer of signal lines or of storage capacitance (Cs) lines are required solely for applying the direct-current voltage on occasion of repairing the luminous dot. Consequently, aperture ratio (a percentage of light transmissive region in each pixel dot) would be decreased; and parasite capacitances would be formed between the wirings solely for applying the direct-current voltage and other wirings, at their crossing points or overlapping regions as to increase load for driving the LCD.
The repairing techniques of the second category also have a problem in that patterns or wirings for severing the pixel electrode from the pattern for pixel capacitance are required, as to decrease the aperture ratio.